1. Field of the Invention
The present invention relates generally to a neighbor cell signal measurement, and in particular, to an apparatus and method for avoiding an unnecessary neighbor cell signal measurement due to a signal change caused by a temporary condition change.
2. Description of the Related Art
The Universal Mobile Telecommunications System (UMTS), which is the third-generation (3G) mobile communication system in Europe, has been providing its commercial services in many countries over the world and the number of subscribers to this service is increasing. The UMTS, which is standardized by the 3rd Generation Partnership Project (3GPP), can more efficiently provide high-speed data/multimedia service than the existing second-generation (2G) mobile communication system and provide an international roaming function available in any place.
The 2G system, Global System for Mobile communications (GSM), has been provided in European countries from the early 1990s. Currently, almost every country in Europe and the United States is providing stable 2G service over nationwide networks.
The UMTS system is serviceable in major cities across the Europe and is expanding its coverage. Since a seamless handover is feasible between the UMTS system and the GSM, a UMTS subscriber can enjoy voice and packet services in any place.
When migrating from one cell of the 3G mobile communication system (the UMTS) to another cell, a terminal performs an intra-frequency or inter-frequency cell reselection. When migrating to a region having no UMTS cell, the terminal performs the cell reselection to a cell of the 2G mobile communication system (the GSM).
The three cell reselection conditions are defined in the standard specification. When the signal level difference between the current serving cell and the other cell meets a certain condition, the cell reselection to the other cell is carried out. Parameters required for the cell reselection are carried by system information (specifically, System Information Block (SIB) 3) broadcast to terminals over the network. The signal measurement conditions for those three cell reselections are shown in Table 1.
TABLE 1TypeSignal strengthIntra CellSqual > Sintrasearch =>Squal <= Sintrasearch =>ReselectionUE need not performUE performintra-frequency measurementintra-frequencymeasurementIf Sintrasearch is not sent for serving cell,perform intra-frequency measurements.Inter CellSqual > Sintersearch =>Squal <= Sintersearch =>ReselectionUE need not performUE performinter-frequency measurementinter-frequencymeasurementIf Sintersearch is not sent for serving cell,perform inter-frequency measurements.Inter.RAT CellSqual >Squal <=ReselectionSsearch.RAT(GSM) =>Ssearch.RAT(GSM) =>UE need not performUE performmeasurement on cellsmeasurement on cells ofof RAT(GSM)RAT(GSM)If Ssearch.RAT(GSM) is no sent for serving cell,perform measurement on cells of RAT(GSM)Squal = Qqualmeas − Qqualmin.
“Qqualmeas” is a measured cell quality value and is calculated in Common Pilot CHannel (CPICH) Energy per chip to Noise ratio (Ec/No) or CPICH Received Signal Code Power (RSCP). “Qqualmin” is a minimum required quality level; that is, a minimum value. “Squal” is a cell selection quality value.
“Sintrasearch” is a threshold for the intra-frequency measurement, “Sintersearch” is a threshold for the inter-frequency measurement, and “Ssearch.RAT(GSM)” is a threshold for inter-Radio Access Technology (RAT) frequency measurement. “Qqualmin”, “Sintrasearch”, “Sintersearch”, and “Ssearch.RAT(GSM)” are delivered to the terminal by the system information (SIB3). When “Sintrasearch” (“Sintersearch” or “Ssearch.RAT(GSM)” is greater than “Squal”, the current specification describes that the terminal performs the cell reselection.
FIG. 1 illustrates a conventional algorithm for the neighbor cell signal measurement.
Specifically, FIG. 1 shows part of an SIB3 parameter of a Vodafone D2 network.
When satisfying the condition of Table 2, the German Vodafone D2 network commences the neighbor cell signal measurement for the intra-frequency cell reselection and the inter-RAT cell reselection.
TABLE 2CaseContentIntra frequency caseCPICH Ec/No - (−18) <= 3 => CPICH Ec/No <=−15 dBInter-RAT caseCPICH Ec/No - (−18) <= 2 => CPICH Ec/No <=−16 dB
When CPICH Ec/No value is less than or equal to −15 dB or −16 dB, the neighbor cell signal measurement for the intra-frequency cell reselection and the inter-RAT cell reselection starts.
Once the signal level of CPICH Ec/No or CPICH RSCP of the current serving cell meets a certain condition, the conventional technique starts the neighbor cell signal measurement. In this case, although the terminal does not travel in the boundary of the current cell, when the received signal level meets the condition for the cell reselection owing to a temporary obstacle around the terminal, the neighbor cell signal measurement commences. However, if the obstacle disappears, the received signal level is regained and thus there is no need to measure the neighbor cell signal.
In other words, when the temporary obstacle causes the temporary decrease of the received signal level though the terminal does not travel in the cell boundary, the unnecessary neighbor cell signal measurement commences.